JP2011069324A - Exhaust emission control device for engine - Google Patents

Abstract

Exhaust purification performance is maintained while suppressing clogging of DPF.
When the vehicle is stopped and the DPF forced regeneration condition is satisfied (S1, 2), the DOC activation temperature is set to the target temperature, and the DOC inlet temperature detected by the sensor is set to the inlet temperature (S3, S3). 4). If the vehicle is not stopped and the DPF forced regeneration condition is satisfied (S1, S10), the DPF regeneration temperature is set to the target temperature, and the DPF inlet temperature detected by the sensor is set to the inlet temperature (S11, 12). . If the vehicle is not stopped and the DPF forced regeneration condition is not satisfied (S1, S10), the SCR activation temperature is set to the target temperature, and the SCR inlet temperature detected by the sensor is set to the inlet temperature (S13, 14). ). If the inlet temperature is equal to or lower than the target temperature (S5), the electric heater disposed upstream of the DOC exhaust is controlled so that the inlet temperature approaches the target temperature (S8, 9).
[Selection] Figure 2

Description

  The present invention relates to an exhaust purification device that purifies PM (particulate matter) and NOx (nitrogen oxide) contained in engine exhaust.

  As described in JP 2009-138680 A (Patent Document 1), as an exhaust purification device for purifying PM and NOx contained in engine exhaust, a continuous regeneration type DPF (Diesel Particulate Filter) device in an exhaust passage, and There have been proposed ones each provided with an SCR (Selective Catalytic Reduction) catalyst. This exhaust purification device continuously collects and removes PM by a continuous regeneration type DPF device, while purifying PM and NOx in exhaust gas simultaneously by selectively reducing and purifying NOx by an SCR catalyst.

JP 2009-138680 A

  By the way, in order to continuously collect and remove PM by the continuous regeneration type DPF device, it is necessary that the DOC (Diesel Oxidation Catalyst) arranged in the preceding stage is heated to an activation temperature or higher. Also, in a continuous regeneration type DPF device, if the exhaust temperature is below the DOC activation temperature for a long time, such as in a low load operation, the ability to generate nitrogen dioxide that promotes the oxidation of PM decreases and the DPF becomes clogged. Therefore, the “forced regeneration process” for forcibly incinerating the PM collected in the DPF is indispensable. At this time, in order to execute the forced regeneration process of the DPF, the DPF needs to be heated to a regeneration temperature or higher. Furthermore, in order to selectively reduce and purify NOx with the SCR catalyst, the SCR catalyst needs to be heated to an activation temperature or higher.

  However, since the activation temperature of the DOC, the regeneration temperature of the DPF, and the activation temperature of the SCR catalyst are different from each other, the exhaust purification performance can be suppressed while suppressing the clogging of the DPF only by applying a known method for raising the exhaust temperature. It was difficult to maintain.

  Therefore, in view of the problems of the prior art, the present invention controls the temperature of the exhaust gas flowing into the DOC, DPF or SCR catalyst by appropriately controlling an electric heater disposed upstream of the exhaust of the continuous regeneration type DPF device, An object of the present invention is to provide an engine exhaust purification device that maintains exhaust purification performance while suppressing clogging of the DPF.

  Therefore, in the present invention, the continuous regeneration type DPF device having the DOC and the DPF, the SCR catalyst disposed downstream of the exhaust gas of the continuous regeneration type DPF device, and the exhaust gas upstream of the continuous regeneration type DPF device. The first temperature detecting means for detecting the exhaust temperature at the inlet of the DOC, the second temperature detecting means for detecting the exhaust temperature at the inlet of the DPF, and the exhaust temperature at the inlet of the SCR catalyst. Third temperature detecting means for detecting, parking determining means for determining whether or not the vehicle is parked, condition determining means for determining whether or not a forced regeneration condition for the DPF is satisfied, and the parking determination When it is determined by the means that the vehicle is parked and the condition determining means determines that the forced regeneration condition is satisfied, the activation temperature of the DOC is set to the target temperature. The exhaust gas temperature detected by the first temperature detection means is set to the inlet temperature, the parking determination means determines that the vehicle is not parked, and the condition determination means sets the forced regeneration condition. A second setting means for setting the regeneration temperature of the DPF to a target temperature and determining the exhaust temperature detected by the second temperature detection means as an inlet temperature when it is determined that the condition is established; When the parking determination means determines that the vehicle is not parked and the condition determination means determines that the forced regeneration condition is not satisfied, the activation temperature of the SCR catalyst is set to a target temperature, and the first And 3rd setting means for setting the exhaust temperature detected by the temperature detecting means 3 to the inlet temperature, and when the inlet temperature is equal to or lower than the target temperature, the inlet temperature approaches the target temperature. Sea urchin, including, a first heater control means for controlling operation of the electric heater constituting the exhaust gas purifying apparatus for an engine.

  According to the present invention, if the vehicle is stationary and the DPF forced regeneration condition is satisfied, the DOC activation temperature is set as the target temperature in order to promote the forced regeneration processing of the DPF while the vehicle is stopped. In addition, the exhaust temperature at the inlet of the DOC is set as the inlet temperature as a control variable. If the vehicle is traveling and the DPF forced regeneration condition is satisfied, the regeneration temperature of the DPF is set as the target temperature in order to promote the forced regeneration processing of the DPF during traveling, The exhaust gas temperature at the DPF inlet is set as the temperature. Further, if the vehicle is traveling and the DPF forced regeneration condition is not satisfied, the activation temperature of the SCR catalyst is set as the target temperature in order to promote the exhaust purification function of the SCR catalyst during traveling. The exhaust gas temperature at the inlet of the SCR catalyst is set as the inlet temperature.

  If the inlet temperature is equal to or lower than the target temperature, the operation of the electric heater is controlled on the basis of the necessary heat generation amount for bringing the inlet temperature close to the target temperature. For this reason, according to the state of the vehicle, the DOC, DPF or SCR catalyst can be brought close to the temperature at which each function is exhibited, and the exhaust purification performance can be maintained while suppressing clogging of the DPF.

Schematic showing an example of an exhaust emission control device embodying the present invention Flow chart showing contents of control program Explanatory drawing of the map for obtaining the required calorific value

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an embodiment of an exhaust emission control device embodying the present invention.
An intake pipe 14 (intake passage) connected to the intake manifold 12 of the diesel engine 10 is provided with an air cleaner 16 that removes dust and the like in the air along the intake circulation direction, a compressor 18A of the turbocharger 18, and a turbocharger 18. An intercooler 20 that cools the intake air that has become hot and an intake collector 22 that smoothes the intake pulsation are arranged in this order.

On the other hand, in the exhaust pipe 26 (exhaust passage) connected to the exhaust manifold 24 of the diesel engine 10, the turbine 18 </ b> B of the turbocharger 18, the continuously regenerating DPF device 28, and the reducing agent precursor are arranged along the exhaust circulation direction. An injection nozzle 30 that injects and supplies urea aqueous solution, an SCR catalyst 32 that selectively reduces and purifies NOx using ammonia generated from the urea aqueous solution, and an oxidation catalyst 34 that oxidizes ammonia that has passed through the SCR catalyst 32 are arranged in this order. Is done. The continuous regeneration type DPF device 28 includes a DOC 28A that oxidizes at least nitric oxide (NO) into nitrogen dioxide (NO ₂ ), and a DPF 28B that collects and removes PM. Instead of DPF 28B, a CSF (Catalyzed Soot Filter) having a catalyst (active component and additive component) supported on the surface thereof may be used.

  The aqueous urea solution stored in the reducing agent tank 36 is supplied to the injection nozzle 30 via a reducing agent addition unit 38 having a built-in pump and flow control valve. Here, the reducing agent addition unit 38 may have a structure divided into two, that is, a pump module with a built-in pump and a dosing module with a built-in flow control valve.

  An electric heater driven by a battery or the like is provided in the exhaust pipe upstream of the continuous regeneration type DPF device 28, that is, in the exhaust pipe 26 located between the turbine 18B and the DOC 28A of the turbocharger 18 in order to forcibly heat the intake air. 40 is disposed.

  As an exhaust purification device control system, an exhaust pipe 26 positioned between the electric heater 40 and the DOC 28A has a temperature sensor 42 (first temperature detecting means) for detecting an exhaust temperature (DOC inlet temperature) at the inlet of the DOC 28A. Is attached. A temperature sensor 44 (second temperature detecting means) for detecting an exhaust temperature (DPF inlet temperature) at the inlet of the DPF 28B is attached to the exhaust pipe 26 positioned between the DOC 28A and the DPF 28B. A temperature sensor 46 (third temperature detecting means) for detecting the exhaust temperature (SCR inlet temperature) at the inlet of the SCR catalyst 32 is attached to the exhaust pipe 26 positioned between the DPF 28B and the injection nozzle 30. In the vicinity of the exhaust pipe 26 where the DPF 28B is disposed, a differential pressure sensor 48 (difference) for detecting the differential pressure upstream and downstream of the DPF 28B in order to determine whether or not the forced regeneration condition of the DPF 28B is satisfied. Pressure detecting means) is attached. Further, a parking brake lever and a transmission (not shown) include a brake switch 50 (operation state detecting means) that is turned on when the parking brake is operated and a neutral switch 52 (shift state detection that is turned on when the parking brake is neutral). Means) are attached respectively. Further, an air flow sensor 54 for detecting an intake air flow rate is attached to the intake pipe 14 positioned between the air cleaner 16 and the compressor 18 </ b> A of the turbocharger 18.

  The output signals of the temperature sensors 42, 44 and 46, the differential pressure sensor 48, the brake switch 50, the neutral switch 52 and the air flow sensor 54 are input to an after treatment control unit (ACU) 56 incorporating a computer. The The ACU 56 is an engine that electronically controls the diesel engine 10 via a CAN (Controller Area Network) or the like so that the rotational speed Ne and the fuel injection amount q as the engine operating state and the vehicle speed v can be appropriately read. A control unit (ECU) 58 is connected. The ACU 56 executes a control program stored in a ROM (Read Only Memory) or the like, thereby electronically controlling the reducing agent addition unit 38 and the electric heater 40 in accordance with output signals from the sensors and the switches. To do. Here, the ECU 58 functions as a rotation speed detection unit, an injection amount detection unit, and a vehicle speed detection unit. However, the rotation speed Ne, the fuel injection amount q, and the vehicle speed v may be directly detected using known sensors. .

In such an exhaust purification device, the exhaust from the diesel engine 10 is introduced into the DOC 28A of the continuous regeneration type DPF device 28 via the exhaust manifold 24 and the turbine 18B of the turbocharger 18. Exhaust introduced into DOC28A flows to DPF28B being oxidized NO is to NO _2. In the DPF 28B, PM in the exhaust gas is collected and the PM is oxidized using NO ₂ generated by the DOC 28A.

Also, the urea aqueous solution supplied (added) from the injection nozzle 30 according to the engine operating state is hydrolyzed using exhaust heat and water vapor in the exhaust, and converted into ammonia that functions as a reducing agent. This ammonia is known to be selectively reduced with NOx in the exhaust gas in the SCR catalyst 32 and purified to harmless water (H ₂ O) and nitrogen (N ₂ ). At this time, NO is oxidized to NO ₂ by the DOC 28A, and the ratio of NO to NO ₂ in the exhaust gas is improved to be suitable for the selective reduction reaction, so that the NOx purification efficiency in the SCR catalyst 32 can be improved. it can. On the other hand, the ammonia that has passed through the SCR catalyst 32 is oxidized by the oxidation catalyst 34 disposed downstream of the exhaust gas, so that it is possible to suppress the ammonia from being released into the atmosphere as it is.

  FIG. 2 shows the contents of a control program for the electric heater 40 that the ACU 56 repeatedly executes at predetermined intervals when the diesel engine 10 is started. The ACU 54 executes the control program so that the parking determination means, the condition determination means, the first setting means, the second setting means, the third setting means, the estimation means, the first heater control means, and the second The heater control means and the deceleration determination means are realized.

  In step 1 (abbreviated as “S1” in the figure, the same applies hereinafter), the vehicle is parked through whether or not the brake switch 50 is ON (parking brake operation) and the neutral switch 52 is ON (neutral). It is determined whether or not. If the vehicle is parked, the process proceeds to step 2 (Yes), while if the vehicle is not parked (that is, if the vehicle is traveling including a temporary stop), the process proceeds to step 10 (No). Here, it is possible to determine with high accuracy that the vehicle is parked by determining that the vehicle is parked when the parking brake is in operation and in neutral. In addition, the process of step 1 corresponds to a parking determination means.

  In step 2, assuming that the vehicle is parked, the forced regeneration condition for starting the forced regeneration process of the DPF 28B is determined based on whether or not the differential pressure detected by the differential pressure sensor 48 is equal to or higher than a predetermined pressure. It is determined whether or not it is established. Here, the predetermined pressure is a threshold for determining that clogging has occurred in the DPF 28B, and is, for example, a pressure slightly lower than the allowable maximum value of the exhaust pressure. If the forced regeneration condition is satisfied, the process proceeds to step 3 (Yes), while if the forced regeneration condition is not satisfied, the process is terminated (No). Note that the processing in step 2 corresponds to the condition determination means.

In step 3, a DOC activation temperature (for example, 250 ° C.) at which the DOC 28A is activated is set as a target temperature for raising the exhaust gas temperature by the electric heater 40.
In step 4, the DOC inlet temperature detected by the temperature sensor 42 is set as the inlet temperature as the control variable. Note that the processing of step 3 and step 4 corresponds to the first setting means.

  In step 5, it is determined whether the inlet temperature is higher than the target temperature. If the inlet temperature is higher than the target temperature, the process proceeds to step 6 (Yes). On the other hand, if the inlet temperature is equal to or lower than the target temperature, the process proceeds to step 9 (No), and the exhaust flow rate and the target temperature are calculated using the calculation formula “required heat generation = exhaust flow rate × specific heat × (target temperature−inlet temperature)”. And the required heat generation according to the inlet temperature is calculated. Here, the exhaust flow rate is estimated based on the engine operating state (the fuel injection amount q and the engine rotation speed Ne read from the ECU 58 and the intake flow rate detected by the air flow sensor 54) in order to prevent an increase in cost and weight due to the addition of the sensor. do it. In addition, the process which estimates exhaust flow volume corresponds to an estimation means.

  In step 6, the vehicle speed v and the fuel injection amount q are read from the ECU 58, and whether the vehicle speed v is greater than 0 (v> 0) and the fuel injection amount q is 0 (q = 0). It is determined whether or not the vehicle is decelerating. If the vehicle speed v is greater than 0 and the fuel injection amount q is 0, the process proceeds to step 7 (Yes), and otherwise, the process is terminated (No). Here, by determining that the vehicle is decelerating when the vehicle speed v is greater than 0 and the fuel injection amount q is 0, it can be recognized in advance that the exhaust gas temperature will subsequently decrease. Note that the processing of step 6 corresponds to the deceleration determination means.

  In step 7, as shown in FIG. 3, referring to a map in which the necessary heat generation amount corresponding to the engine rotation speed is set, the necessary heat generation amount that matches the engine rotation speed Ne read from the ECU 58 is obtained. Here, the necessary amount of heat set in the map is the amount of heat necessary for maintaining the inlet temperature at the target temperature in anticipation of the exhaust temperature gradually decreasing because the vehicle is decelerating. Moreover, the increase in control load of the ACU 56 can be suppressed by obtaining the required heat generation amount with reference to the map.

  In step 8, the operation of the electric heater 40 is controlled based on the required heat generation amount. That is, the operation of the electric heater 40 is controlled so that the inlet temperature approaches the target temperature or the inlet temperature is maintained at the target temperature. Note that the processing of Step 5, Step 8 and Step 9 corresponds to the first heater control means, while the processing of Step 5, Step 7 and Step 8 corresponds to the second heater control means.

  In step 10, on the assumption that the vehicle is running, the forced regeneration condition for starting the forced regeneration process of the DPF 28B is determined based on whether or not the differential pressure detected by the differential pressure sensor 48 is equal to or higher than a predetermined pressure. It is determined whether or not it is established. If the forced regeneration condition is satisfied, the process proceeds to step 11 (Yes), while if the forced regeneration condition is not satisfied, the process proceeds to step 13 (No). In addition, the process of step 10 corresponds to a condition determination means.

In step 11, a DPF regeneration temperature (for example, 300 ° C.) regenerated by the DPF 28 </ b> B is set as a target temperature for increasing the exhaust gas temperature by the electric heater 40.
In step 12, the DPF inlet temperature detected by the temperature sensor 44 is set as the inlet temperature as a control variable, and then the process proceeds to step 5. In addition, the process of step 11 and step 12 corresponds to a 2nd setting means.

In step 13, an SCR activation temperature (for example, 220 ° C.) at which the SCR catalyst 34 is activated is set as a target temperature for increasing the exhaust temperature by the electric heater 40.
In step 14, the SCR inlet temperature detected by the temperature sensor 46 is set as the inlet temperature as a control variable, and then the process proceeds to step 5. Note that the processing of step 13 and step 14 corresponds to the third setting means.

  According to such an exhaust purification device, when the vehicle is stopped and the forced regeneration condition of the DPF 28B is satisfied, the DOC activation temperature is set as the target temperature in order to promote the forced regeneration processing of the DPF 28B while the vehicle is stopped. At the same time, the DOC inlet temperature is set as the inlet temperature as a control variable. Further, if the vehicle is traveling and the forced regeneration condition of the DPF 28B is satisfied, the DPF regeneration temperature is set as the target temperature and the inlet temperature to promote the forced regeneration processing of the DPF 28B during traveling. As a result, the DPF inlet temperature is set. Further, if the vehicle is traveling and the forced regeneration condition of the DPF 28B is not satisfied, the SCR activation temperature is set as the target temperature to promote the exhaust purification function of the SCR catalyst 32 during traveling, The SCR inlet temperature is set as the inlet temperature.

  If the inlet temperature is equal to or lower than the target temperature, the operation of the electric heater 40 is controlled based on the necessary heat generation amount for bringing the inlet temperature close to the target temperature. For this reason, according to the state of the vehicle, the DOC 28A, DPF 28B or SCR catalyst 32 can be brought close to the temperature at which each function is exhibited, and the exhaust purification performance can be maintained while suppressing clogging of the DPF 28B.

  Further, if the inlet temperature is higher than the target temperature and the vehicle is decelerating, the operation of the electric heater 40 is controlled based on the necessary heat generation amount corresponding to the engine rotational speed Ne. That is, since the engine load is small when the vehicle is decelerating, the exhaust temperature gradually decreases and falls below the target temperature. For this reason, by controlling the operation of the electric heater 40 based on the required heat generation amount that maintains the inlet temperature at the target temperature, the inlet temperature is prevented from lowering below the target temperature, and the exhaust purification performance is reduced. Can be suppressed.

10 Diesel engine 28 Continuous regeneration type DPF device 28A DOC
28B DPF
32 SCR catalyst 40 Electric heater 42 Temperature sensor 44 Temperature sensor 46 Temperature sensor 48 Differential pressure sensor 50 Brake switch 52 Neutral switch 54 Air flow sensor 56 ACU
58 ECU

Claims (7)

A continuously regenerating DPF device having a DOC and a DPF;
An SCR catalyst disposed downstream of the exhaust of the continuous regeneration type DPF device;
An electric heater disposed upstream of the exhaust of the continuous regeneration type DPF device;
First temperature detection means for detecting an exhaust temperature at the inlet of the DOC;
Second temperature detecting means for detecting the exhaust temperature at the inlet of the DPF;
Third temperature detection means for detecting the exhaust temperature at the inlet of the SCR catalyst;
Parking determination means for determining whether or not the vehicle is parked;
Condition determination means for determining whether or not the DPF forced regeneration condition is satisfied;
When the parking determination means determines that the vehicle is parked and the condition determination means determines that the forced regeneration condition is satisfied, the activation temperature of the DOC is set to a target temperature, and the first First setting means for setting the exhaust gas temperature detected by one temperature detection means to the inlet temperature;
When the parking determination means determines that the vehicle is not parked and the condition determination means determines that the forced regeneration condition is satisfied, the regeneration temperature of the DPF is set to a target temperature, and the second Second setting means for setting the exhaust gas temperature detected by the temperature detecting means to the inlet temperature;
When the parking determination means determines that the vehicle is not parked and the condition determination means determines that the forced regeneration condition is not satisfied, the activation temperature of the SCR catalyst is set to a target temperature, and the first 3rd setting means for setting the exhaust gas temperature detected by the temperature detecting means of 3 to the inlet temperature;
First heater control means for controlling the operation of the electric heater so that the inlet temperature approaches the target temperature when the inlet temperature is equal to or lower than the target temperature;
An exhaust emission control device for an engine characterized by comprising: An estimation means for estimating the exhaust flow rate based on the engine operating state;
The first heater control means calculates a required heat generation amount corresponding to the target temperature, the inlet temperature, and the exhaust flow rate estimated by the estimation means, and controls the operation of the electric heater based on the required heat generation amount. The engine exhaust gas purification apparatus according to claim 1. An operating state detecting means for detecting an operating state of the parking brake;
Shift state detecting means for detecting a shift state of the transmission;
Further comprising
The parking determination means detects when the parking brake is operated by the operating state detecting means, and when the transmission state detecting means detects that the transmission is being shifted to neutral. The engine exhaust gas purification apparatus according to claim 1 or 2, wherein the vehicle is determined to be parked. A differential pressure detecting means for detecting a differential pressure between the exhaust upstream of the DPF and the exhaust downstream;
The condition determining means determines that the forced regeneration condition of the DPF is satisfied when the differential pressure detected by the differential pressure detecting means is equal to or higher than a predetermined pressure. 4. The exhaust emission control device for an engine according to any one of 3 above. A rotational speed detecting means for detecting the engine rotational speed;
Deceleration determining means for determining whether or not the vehicle is decelerating;
The engine detected by the rotational speed detecting means so that the inlet temperature is maintained at the target temperature when the inlet temperature is higher than the target temperature and the deceleration determining means determines that the engine is decelerating. Second heater control means for controlling the operation of the electric heater in accordance with the rotational speed;
The exhaust emission control device for an engine according to any one of claims 1 to 4, further comprising:   The second heater control means refers to a map in which a required heat generation amount corresponding to the engine rotation speed is set, obtains a required heat generation amount suitable for the engine rotation speed detected by the rotation speed detection means, and 6. The engine exhaust gas purification apparatus according to claim 5, wherein the operation of the electric heater is controlled based on a calorific value. Vehicle speed detection means for detecting the vehicle speed;
Injection amount detection means for detecting the fuel injection amount;
Further comprising
The deceleration determination means determines that the vehicle is decelerating when the vehicle speed detected by the vehicle speed detection means is greater than 0 and the fuel injection amount detected by the injection amount detection means is 0. The engine exhaust gas purification apparatus according to claim 5 or 6, characterized in that:

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